The invention relates to improvements in apparatus, known as sealers or band sealers, which can be utilized in machines for the making of rod-shaped products of the tobacco processing industry to heat and thus stabilize or strengthen the adhesive-containing seams of tubular wrappers for rod-like fillers of tobacco, filter material for tobacco smoke or other material of the tobacco processing industry. For example, the improved apparatus can be utilized to stabilize the longitudinally extending seam of a tubular wrapper which consists of cigarette paper and surrounds a rod-like filler of natural, reconstituted and/or artificial tobacco while the filler advances from a wrapping mechanism to a so-called cutoff of a cigarette rod making machine.
The purpose of the sealer is to condition the moving adhesive-containing seam of the tubular wrapper for the purpose of heating the adhesive in the seam. This causes a water-base adhesive to set or liquefies an adhesive of the type known as hot melt. As a rule, an elongated heated strip-shaped heating device is maintained in actual contact with the exposed outer side of the outer layer of the moving seam.
The strip-shaped heating devices of conventional sealers are made of a metallic material and are connected with heating cartridges which, as a rule, are installed at a considerable distance from the locus of contact between the heating device and the seam. This renders it necessary to employ cartridges whose thermal output is relatively high which, in turn, brings about serious problems during certain stages of operation of such conventional sealers. Thus, the seam portion which contacts the sealer when a cigarette maker is brought to a halt is likely to be overheated and a seam portion which is caused to move along the sealer immediately after the cigarette maker is started or restarted is likely to be heated to a temperature well below the optimum temperature for the particular adhesive. An overheating of te seam is likely to entail charring or other undesirable consequences involving an undesirable change of appearance and/or the strength of the overheated portion of the seam. On the other hand, underheating of the seam can adversely affect the strength of the respective portion of the seam, i.e., the seam is likely to open up during advancement through the cutoff which is located downstream of the sealer as considered in the direction of advancement of a wrapped rod-like filler in a cigarette maker or another rod making machine of the tobacco processing industry.
Another drawback of conventional sealers is that losses due to undesirable heat radiation are very high. Furthermore, the temperature of a conventional sealer cannot be regulated with a desired degree of accuracy and/or within a short or very short interval of time. The reason is that the thermal inertia of conventional sealers is too pronounced. Still another drawback of conventional sealers which include metallic seam-contacting portions is that such portions are likely to become distorted in response to unavoidable fluctuations of their temperature; this can result in the development of unsatisfactory contact between the metallic portion and the moving seam.
U.S. Pat. No. 3,575,766 granted Apr. 20, 1971 to McArthur et al. discloses a band sealer for a cigarette or filter maker wherein the moving seam of a tubular wrapper of cigarette paper or the like is contacted by a thin strip consisting of a metallic material. The strip conducts electric current and forms part of an electric resistance heater, i.e., the heat to be transmitted to the seam is generated directly in the metal strip.